Pictures disappearing

Hi all

I have a strange problem. On one scene in my articulate 2 project the pictures are disappearing from the editing screen and the previewed slide; they are still on the thumbnail unless I open the slide too many times in which case they disappear from there too. The other 14 scenes are fine (the trouble is with scene 12 by the way) and I have closed the file a number of times and re-opened (without saving) and the problem recurs.

I can't see any logical difference between scene 12 and the other 14, so really puzzled. Two screen shots attached to prove I've not gone mad!

Any ideas gratefully received. Nigel